Studies on Ionic Salt of Polyamic Acid and Related Compounds

Amic acid compound namely bisphthalamic acid of 2, 2′-dimethyl-4, 4′-diaminobiphenyl (amic acid) and its ionic salt with 3-(dimethylamino)propyl methacrylate (amic acid salt) were synthesized and characterized by FT-IR, mass spectroscopy, NMR and DSC. Effect of temperature and water content on these compounds was studied by 1H-NMR and potentiometric titration. In the absence of added water, both amic acid and its ionic salt had undergone imidization followed by hydrolysis, which was attributed to the water formed as a result of an initial imidization reaction. Polyamic acid (PAA) was synthesized by reacting 4, 4′-oxydiphthalic anhydride and 2, 2′-dimethyl 4, 4′-diaminobiphenyl (m-tolidine) in N-methyl-2-pyrrolidone, which was then reacted with 3-(dimethylamino)propyl methacrylate to obtain PAS. Their storage stabilities were studied by monitoring their bulk viscosities and acid numbers as a function of time and temperature. PAS was found to be less stable than PAA. Similar observations were made for amic acid compounds. PAA and PAS showed two-step thermal degradation in air and nitrogen.